Catalyst for synthesis gas conversion to oxygenates

ABSTRACT

The conversion of synthesis gas comprising hydrogen and carbon oxides to form oxygenate-containing mixtures which are limited compositionally in being virtually free of C 11  + compounds, with a zeolite which is virtually free of acid sites and characterized by a silica to alumina mole ratio of at least about 12 and a constraint index within the range of 1 to 12, having intimately combined therewith a metal selected from the group consisting of rhodium, platinum, palladium and iridium.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 065,821 filedAug. 13, 1979 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is concerned with a process for converting synthesis gascomprising hydrogen and carbon oxides to form a product comprising asubstantial proportion of organic oxygenates. In one aspect, thisinvention is concerned with a process for converting synthesis gascomprising hydrogen and carbon oxides to form mixtures of oxygenates andhydrocarbons, which are limited compositionally in being virtually freeof C₁₁ + compounds. In another aspect, this invention is concerned withproviding a novel catalyst composition for the conversion of synthesisgas to a product comprising a substantial proportion of organicoxygenates, which is limited compositionally in being virtually free ofC₁₁ + compounds.

2. Prior Art

Processes for the conversion of coal and other hydrocarbons such asnatural gas to a gaseous mixture consisting essentially of hydrogen andcarbon monoxide, or of hydrogen and carbon dioxide, or of hydrogen andcarbon monoxide and carbon dioxide, are well known. Although variousprocesses may be employed for the gasification of carbonaceous fuels,those of major importance depend either on the partial combustion of thefuel with an oxygen-containing gas or on the high temperature reactionof the fuel with steam, or on a combination of these two reactions. Anexcellent summary of the art of gas manufacture, including synthesisgas, from solid and liquid fuels, is given in the ENCYCLOPEDIA OFCHEMICAL TECHNOLOGY, Edited by Kirk-Othmer, Second Edition, Volume 10,pages 353-433 (1966), Interscience Publishers, New York, N.Y., thecontents of which are herein incorporated by reference. The techniquesfor gasification of coal or other solid, liquid or gaseous fuel are notconsidered to be per se inventive here.

It would be very desirable to be able to effectively convert synthesisgas, and thereby coal and natural gas, to highly valued fuels such asmotor gasoline with high octane number and chemical intermediates. It iswell known that synthesis gas will undergo conversion to form reductionproducts of carbon monoxide, such as hydrocarbons and alcohols, at fromabout 300° F. to about 850° F. under pressure from about 1 to 1000atmospheres, over a fairly wide variety of catalysts. TheFischer-Tropsch process, for example, which has been most extensivelystudied, produces a range of liquid hydrocarbons, a portion of whichhave been used as low octane gasoline. The types of catalysts that havebeen studied for this and related processes include those based onmetals or oxides of zinc, iron, cobalt, nickel, ruthenium, thorium,rhodium and osmium.

Catalysts based on ZnO are particularly suited for the production ofmethanol and dimethyl ether. Catalysts based on Fe, Co, and Ni, andespecially Fe, are particularly suited for the production of oxygenatedand hydrocarbon products that have at least one carbon-to-carbon bond intheir structure. With the exception of ruthenium, all practicalsynthesis catalysts contain chemical and structural promoters. Thesepromoters include copper, chromia, alumina and alkali. Alkali is ofparticular importance with iron catalysts, since it greatly enhances theconversion efficiency of the iron catalyst. Supports such as kieselguhrsometimes act beneficially.

The catalyzed reduction of carbon monoxide or carbon dioxide by hydrogenproduces various oxygenated and hydrocarbon products, depending on theparticular catalyst and reaction conditions chosen. The products thatare formed include methanol; dimethyl ether; acetone; acetic acid;normal propyl alcohol; higher alcohols; methane; gaseous, liquid andsolid olefins and paraffins. It should be noted that this spectrum ofproducts consists of aliphatic compounds; aromatic hydrocarbon eitherare totally absent or are formed in minor quantities.

In general, when operating at the lower end of the temperature range,i.e. from about 300° F. to about 500° F., in the reduction of carbonmonoxide, and with pressures greater than about 20 atmospheres,thermodynamic considerations suggest that aliphatic hydrocarbons arelikely to form in preference to their aromatic counterparts.Furthermore, in some catalytic systems it has been noted that aromatichydrocarbon impurities in the synthesis gas inactivate the synthesiscatalyst, and one may speculate that a number of known synthesiscatalysts intrinsically are not capable of producing aromatichydrocarbons.

The wide range of catalysts and catalyst modifications disclosed in theart and an equally wide range of conversion conditions for the reductionof carbon monoxide by hydrogen provide considerable flexibility towardobtaining selected boiling range products. Nonetheless, in spite of thisflexibility, it has not proved possible to make such selections so as toproduce oxygenates or mixtures of oxygenates and hydrocarbons which arelimited compositionally in being virtually free of C₁₁ + compounds. Areview of the status of this art is given in Carbon Monoxide-HydrogenReactions, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Edited by Kirk-Othmer,Second Edition, Volume 4, pages 446-488, Interscience Publishers, NewYork, N.Y., the text of which is incorporated herein by reference.

Recently it has been discovered that synthesis gas may be converted tooxygenated organic compounds and these then converted to higherhydrocarbons, particularly high octane gasoline, by catalytic contact ofthe synthesis gas with a carbon monoxide reduction catalyst followed bycontacting the conversion products so produced with a special type ofzeolite catalyst in a separate reaction zone. This two-stage conversionis described in U.S. Pat. No. 4,076,761.

Another process to produce high octane gasoline is disclosed in U.S.Pat. No. 3,972,958. In this process, coal is gasified and the resultantsynthesis gas from the gasification is converted into high octanearomatic gasoline and light hydrocarbon gases.

The conversion of synthesis gas to hydrocarbon mixtures is described inU.S. Pat. Nos. 4,086,252 and 4,096,163. These patents involve the use ofacidic crystalline zeolites in admixture with carbon oxide reducingcomponents, such as Fischer-Tropsch catalysts. Conversion of synthesisgas to hydrocarbon mixtures is also described in U.S. Pat. No.4,157,338.

Copending U.S. patent application Ser. No. 926,987 filed July 21, 1978,now U.S. Pat. No. 4,172,843, describes conversion of syngas to olefinicnaphtha utilizing a catalyst comprising an iron containingFischer-Tropsch Component and a substantially non-acidic ZSM-5 typezeolite.

Compositions of iron, cobalt or nickel deposited in the inner absorptionregions of crystalline zeolites are described in U.S. Pat. No.3,013,990. Attempts to convert synthesis gas over X-zeolite baseexchanged with iron, cobalt and nickel are described in Erdoel undKohle--ERDGAS, PETROCHEMIE: BRENNSTOFF--CHEMIE, Volume 25, No. 4, pages187-188, April 1972.

It is an object of the present invention to provide an improved processfor converting fossil fuels to mixtures of hydrocarbons and oxygenatescontaining large quantities of high desirable constituents. It is afurther object of this invention to provide a more efficient method forconverting a mixture of gaseous carbon oxides and hydrogen to form aproduct comprising a substantial proportion of organic oxygenates. It isa further object of this invention to provide an improved method forconverting synthesis gas to mixtures of hydrocarbons and oxygenateswhich are virtually free of C₁₁ + compounds. It is a further object ofthis invention for converting synthesis gas to high octane gasoline andoxygenates which may be valuable as chemical intermediates. It is afurther object of this invention to provide novel catalysts for theconversion of synthesis gas.

SUMMARY OF THE INVENTION

It has now been discovered that valuable oxygenate containing mixturescan be produced by reacting synthesis gas, i.e., mixtures of hydrogengas with gaseous carbon oxides, or the equivalents of such mixtures, inthe presence of certain catalysts. The catalysts, as will be more fullydescribed hereinafter, are those in which a novel class of zeolitescharacterized by a silica to alumina mole ratio of at least 12 and aconstraint index within the range of 1 to 12 and which is virtually freeof acid sites (i.e. substantially non-acidic) and having intimatelycombined therewith a metal selected from the group consisting ofrhodium, platinum, palladium and iridium, preferably rhodium.

Depending on the catalyst and the particular reaction conditions, onemay obtain substantial quantities of liquid mixtures which are rich inoxygenates and are limited compositionally in being virtually free ofC₁₁ + compounds and thus eminently suited for use as a high octanegasoline or chemical intermediate. Oxygenate products so obtainedcomprise alcohols, esters, ketones, aldehydes and acids.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

Synthesis gas for use in this invention consists of a mixture ofhydrogen gas with gaseous carbon oxides, including carbon monoxide andcarbon dioxide. By way of illustration, a typical purified synthesis gaswill have the composition, on a water-free basis, in volume percentages,as follows: hydrogen 51; carbon monoxide, 40; carbon dioxide, 4;methane, 1; and nitrogen, 4.

The synthesis gas may be prepared from fossil fuels by any of the knownmethods, including such in-situ gasification processes as theunderground partial combustion of coal and petroleum deposits. The term"fossil fuels", as used herein, is intended to include anthracite andbituminous coal, lignite, crude petroleum, shale oil, oil from tarsands, natural gas, as well as fuels derived from simple physicalseparations or more profound transformations of these materials,including coked coal, petroleum coke, gas oil, residua from petroleumdistillation, and two or more of any of the foregoing materials incombination. Other carbonaceous fuels such as peat, wood and cellulosicwaste materials also may be used.

The raw synthesis gas produced from fossil fuels will contain variousimpurities such as particulates, sulfur, ammonia and metal carbonylcompounds, and will be characterized by hydrogen-to-carbon oxides ratioswhich will depend on the fossil fuel and the particular gasificationtechnology utilized. In general, it is desirable for the efficiency ofthe subsequent conversion steps to purify the raw synthesis gas by theremoval of impurities. Techniques for such purification are known andare not part of this invention. Furthermore, it may be required toadjust the hydrogen-to-carbon oxides volume ratio to be within apreferred range prior to use in this invention. Should the purifiedsynthesis gas be excessively rich in carbon oxides, it may be broughtwithin the preferred range by the well known water-gas shift reaction.On the other hand, should the synthesis gas be excessively rich inhydrogen, it may be adjusted into the preferred range by the addition ofcarbon dioxide or carbon monoxide.

It is contemplated that the synthesis gas for use in this inventionincludes art-recognized equivalents to the already-described mixtures ofhydrogen gas with gaseous carbon oxides. Mixtures of carbon monoxide andsteam, for example, or of carbon dioxide and hydrogen, to provideadjusted synthesis gas by in-situ reaction, are contemplated.

The catalysts of this invention comprise a novel class of zeolites whichis virtually free of acid sites, i.e. substantially non-acidic, havingintimately combined therewith a metal selected from the group consistingof rhodium, platinum, palladium and iridium, with rhodium beingparticuarly preferred. The novel class of zeolites of this invention ischaracterized by a silica to alumina mole ratio of at least 12 and aconstraint index, as defined hereinafter, within the range of 1 to 12.

An important characteristic of the crystal structure of this novel classof zeolites is that it provides constrained access to, and egress from,the intracrystalline free space by virtue of having a pore sizeintermediate between the small pore Linde A and the large pore Linde X,i.e. the pore windows of the structure are of about a size such as wouldbe provided by ten-membered rings of silicon atoms interconnected byoxygen atoms. It is to be understood, of course, that these rings arethose formed by the regular disposition of the tetrahedra making up theanionic framework of the crystalline zeolite, the oxygen atomsthemselves being bonded to the silicon or aluminum atoms at the centersof the tetrahedra.

The silica to alumina mole ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminamole ratio of at least 12 are useful, it is preferred in many instancesto use zeolites having much higher silica to alumina mole ratios. Inaddition, zeolites as otherwise characterized herein but which aresubstantially free of aluminum, i.e. having high silica to alumina moleratios which range up to and including infinity, are found to be usefuland even preferable in some instances. Such "high silica" or "highlysiliceous" zeolites are intended to be included within this description.The novel class of zeolites, after activation, acquire anintracrystalline sorption capacity for normal hexane which is greaterthan that for water, i.e. they exhibit "hydrophobic" properties. Thishydrophobic character can be used to advantage in some applications.

The novel class of zeolites useful in this invention freely sorb normalhexane and have a pore dimension greater than about 5 Angstroms. Inaddition, the structure must provide constrained access to largermolecules. It is sometimes possible to judge from a known crystalstructure whether such constrained access exists. For example, if theonly pore windows in a crystal are formed by eight-membered rings ofsilicon and aluminum atoms, then access to molecules of largercross-section than normal hexane is excluded and the zeolite is not ofthe desired type. Windows of ten-membered rings are preferred, althoughexcessive puckering or pore blockage may render these catalystsineffective. Twelve-membered rings do not generally appear to offersufficient constraint to produce the advantageous conversions desired inthe instant invention, although structures can be conceived, due to poreblockage or other cause, that may be operative.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access, a simpledetermination of the "Constraint Index" may be made by continuouslypassing a mixture of equal weight of normal hexane and 3-methylpentaneover a small sample, approximately 1 gram or less, of zeolite atatmospheric pressure according to the following procedure. A sample ofthe zeolite, in the form of pellets or extrudate, is crushed to aparticle size about that of coarse sand and mounted in a glass tube.Prior to testing, the zeolite is treated with a stream of air at 1000°F. for at least 15 minutes. The zeolite is then flushed with helium andthe temperature adjusted between 550° F. and 950° F. to give an overallconversion between 10% and 60%. The mixture of hydrocarbons is passed at1 liquid hourly space velocity (i.e., 1 volume of liquid hydrocarbon pervolume of catalyst per hour) over the zeolite with a helium dilution togive a helium to total hydrocarbon mole ratio of 4:1. After 20 minuteson stream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromatography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

While the above experimental procedure will enable one to achieve thedesired overall conversion of 10 to 60% for most samples and representspreferred conditions, it may occasionally be necessary to use somewhatmore severe conditions for samples of very low activity, such as thosehaving a very high silica to alumina mole ratio. In those instances, atemperature of up to about 1000° F. and a liquid hourly space velocityof less than one, such as 0.1 or less, can be employed in order toachieve a minimum total conversion of about 10%.

There also may be situations where the activity is so low, i.e. silicato alumina mole ratio approaching infinity or zeolites with virtually noacid sites, that the constraint index cannot be adequately measured, ifat all. In such situations, Constraint Index is meant to mean theConstraint Index of the exact same substance (i.e. same crystalstructure as determined by such means as X-ray diffraction pattern), butin a measureable form (i.e. acid or aluminum containing form).

The "Constraint Index" is calculated as follows: ##EQU1##

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a Constraint Index from about 1.0 to 12.0.Constraint Index (C.I.) values for some typical zeolites, including somenot within the scope of this invention, are:

    ______________________________________                                                          C.I.                                                        ______________________________________                                        ZSM-4               0.5                                                       ZSM-5               8.3                                                       ZSM-11              8.7                                                       ZSM-12              2.0                                                       ZSM-23              9.1                                                       ZSM-35              4.5                                                       ZSM-38              2.0                                                       TMA Offretite       3.7                                                       Beta                0.6                                                       ZSM-4               0.5                                                       Acid Mordenite      0.5                                                       (H-Zeolon)                                                                    REY                 0.4                                                       Amorphous Silica-Alumina                                                                          0.6                                                       Erionite            38                                                        Clinoptilolite      3.4                                                       ______________________________________                                    

The above-described Constraint Index is an important and even a criticaldefinition of those zeolites which are useful to catalyze the instantprocess. The very nature of this parameter and the recited technique bywhich it is determined, however, admit of the possibility that a givenzeolite can be tested under somewhat different conditions and therebyhave different Constraint Indexes. Constraint Index seems to varysomewhat with severity of operation (conversion) and the presence orabsence of binders. Likewise, other variables such as crystal size ofthe zeolite, the presence of occluded contaminants, etc., may affect theConstraint Index. Therefore, it will be appreciated that it may bepossible to so select test conditions as to establish more than onevalue in the range of 1 to 12 for the Constraint Index of a particularzeolite. Such a zeolite exhibits the constrained access as hereindefined and is to be regarded as having a Constraint Index in the rangeof 1 to 12. Also contemplated herein as having a Constraint Index in therange of 1 to 12 and therefore within the scope of the defined novelclass of highly siliceous zeolites are those zeolites which, when testedunder two or more sets of conditions within the above-specified rangesof temperature and conversion, produce a value of the Constraint Indexslightly less than 1, e.g. 0.9, or somewhat greater than 12, e.g. 14 or15, with at least one other value within the range of 1 to 12.

Thus, it should be understood that "Constraint Index" as such value isused herein is an inclusive rather than an exclusive value. That is, azeolite when tested by any combination of conditions within the testingdefinition set forth hereinabove to have a constraint index of about 1to 12 is intended to be included in the instant novel zeolite definitionregardless that the same identical crystalline zeolite tested underother defined conditions may give a Constraint Index value outside ofthe range of 1 to 12.

In a preferred aspect of this invention, the zeolites useful herein areselected as those having a crystal framework density, in the dryhydrogen form, of not substantially below about 1.6 grams per cubiccentimeter. It has been found that zeolites which satisfy all three ofthese criteria are most desired. Therefore, the preferred catalysts ofthis invention are those comprising zeolites having a Constraint Indexas defined above of about 1 to 12, a silica to alumina mole ratio of atleast about 12 and a dried crystal density of not substantially lessthan about 1.6 grams per cubic centimeter. The dry density for knownstructures may be calculated from the number of silicon plus aluminumatoms per 1000 cubic Angstroms, as given, e.g., on page 19 of thearticle on Zeolite Structure by W. M. Meier. This paper, the entirecontents of which are incorporated herein by reference, is included inProceedings of the Conference on Molecular Sieves, London, April 1967,published by the Society of Chemical Industry, London, 1968. When thecrystal structure is unknown, the crystal framework density may bedetermined by classical pycnometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. It is possible thatthe unusual sustained activity and stability of this class of zeolitesare associated with its high crystal anionic framework density of notless than about 1.6 grams per cubic centimeter. This high density ofcourse must be associated with a relatively small amount of free spacewithin the crystal, which might be expected to result in more stablestructures. This free space, however, seems to be important as the locusof catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                        Void         Framework                                        Zeolite         Volume       Density                                          ______________________________________                                        Ferrierite      0.28   cc/cc     1.76 g/cc                                    Mordenite       .28              1.7                                          ZSM-5, -11      .29              1.79                                         ZSM-12          --               1.79                                         ZSM-23          --               1.80                                         Dachiardite     .32              1.72                                         L               .32              1.61                                         Clinoptilolite  .34              1.71                                         Laumontite      .34              1.77                                         ZSM-4 (Omega)   .38              1.65                                         Heulandite      .39              1.69                                         P               .41              1.57                                         Offretite       .40              1.55                                         Levynite        .40              1.54                                         Erionite        .35              1.51                                         Gmelinite       .44              1.46                                         Chabazite       .47              1.45                                         A               .5               1.3                                          Y               .48              1.27                                         ______________________________________                                    

The novel class of zeolites defined herein is exemplified by ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and other similar materials.

ZSM-5 is more particularly described in U.S. Pat. No. 3,702,886, theentire contents of which are incorporated herein by reference.

ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, theentire contents of which are incorporated herein by reference.

ZSM-12 is more particularly described in U.S. Pat. No. 3,832,449, theentire contents of which are incorporated herein by reference.

ZSM-23 is more particularly described in U.S. Pat. No. 4,076,842, theentire contents of which are incorporated herein by reference.

ZSM-35 is more particularly described in U.S. Pat. No. 4,016,245, theentire contents of which are incorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859, theentire contents of which are incorporated herein by reference.

It is to be understood that by incorporating by reference the foregoingpatents to describe examples of specific members of the novel class withgreater particularity, it is intended that identification of the thereindisclosed crystalline zeolites be resolved on the basis of theirrespective X-ray diffraction patterns. As discussed above, the presentinvention contemplates utilization of such catalysts wherein the moleratio of silica to alumina is essentially unbounded. The incorporationof the identified patents should therefore not be construed as limitingthe disclosed crystalline zeolites to those having the specific silicato alumina mole ratios discussed therein, it now being known that suchzeolites may be substantially aluminum-free and yet, having the samecrystal structure as the disclosed materials, may be useful or evenpreferred in some applications. It is the crystal structure, asidentified by the X-ray diffraction "fingerprint", which establishes theidentity of the specific crystalline zeolite material.

The specific crystalline zeolites described, when prepared in thepresence of organic cations, are substantially inactive, possiblybecause the intracrystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 1000° F. for 1 hour, for example, followed by baseexchange with ammonium salts, followed by calcination at 1000° F. inair. The presence of organic cations in the forming solution may not beabsolutely essential to the formation of this special type zeolite;however, the presence of these cations does appear to favor theformation of this special type of zeolite. More generally, it isdesirable to activate this type zeolite by base exchange with ammoniumsalts, followed by calcination in air at about 1000° F. for from about15 minutes to about 24 hours.

Natural zeolites may sometimes be converted to this type zeolite byvarious activation procedures and other treatments such as baseexchange, steaming, alumina extraction and calcination, alone or incombinations. Natural minerals which may be so treated includeferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulanditeand clinoptilolite.

The instant invention is concerned with a substantially non-acidiczeolite which is virtually free of acidic sites. Without wishing to bebound by any particular theory of operability, it is believed that theusefulness of substantially non-acidic zeolites lies in their ability toinfluence the selectivity or course of reactions by taking advantage ofthe particular pore diameters of the zeolite. Thus, this invention isnot at all concerned with conventional acidic zeolite catalysis, butrather relies on the sieving function of zeolites.

There are various ways in order to arrive at a zeolite which isvirtually free of acidic sites. One way to arrive at a substantiallynon-acidic zeolite is to use a high-silica zeolite. It is known in theart that the greater the aluminum content of a zeolite which is presentin the skeletal structure, the greater the opportunity there is to haveexchangeable sites which can be acidic. Conversely, the lower thealuminum content, the less availability there is to provide acid sitesvia base exchange or other techniques. The zeolite component of thecatalyst of this invention which is substantially free of alumina maycontain minor amounts of such oxide attributable primarily to thepresence of aluminum impurities in the reactants, the atmosphere, and/orthe equipment employed in preparing them. Preparation of a high silicamaterial which may be employed herein is described in U.S. Pat. No.3,941,871, the entire contents of which is incorporated by referenceherein. That patent provides a family of materials which are essentiallyfree of the metals of Group III, e.g. aluminum, gallium, and arecharacterized by an X-ray diffraction pattern characteristic of ZSM-5.

A technique that can be applied to the novel class of zeolites of thepresent invention to arrive at a substantially non-acidic zeolite is toneutralize an acidic zeolite by means of base exchange. Such baseexchange can be accomplished with cations from the group consisting ofthe metals of Group IA of the Periodic Chart of the Elements (FisherScientific Company, Cat. No. 5-702-10, 1978), i.e. Li, Na, K, Rb, Cs,Fr, preferably Na. Also base exchange can be carried out with theelements of Group IIA of the Periodic Chart, i.e., Be, Mg, Ca, Sr, Ba,Ra and also with ammonium ions. Another technique to reduce acidity isto steam the acidic form of the catalyst at high temperatures, e.g.temperatures of 1000° F. and greater.

A special test has been devised to measure the acidity of variouszeolite catalyst components in order to determine whether or not theyare operable in the novel process of this invention. The test involvesmeasure of the rate of cyclopropane isomerization and comparing itagainst 46 A.I. silica-alumina as a reference standard.

The test procedure involves utilizing a 5 to 50 mg sample having aparticle size of 20 to 200 mesh and mixing the same with about 1 ml ofVycor chips and loading into a 5 mm inside diameter Vycor reactor tubewhich is heated in air at a flow rate of 150 ml per minute to 538° C.and maintained there for 30 minutes. The sample is then cooled to 250°C. in helium at a flow rate of 12-80 ml per minute. Cyclopropane(helium/cyclopropane, 4 vol. to vol.) is then introduced and the reactoreffluent analyzed by gas chromatographic techniques. The contact time isadjusted to keep the conversion with 0.5 to 50%. Since it is well knownin the literature that the isomerization of cyclopropane is first order,rate constants may be determined at several temperatures to check fordiffusional limitations. Using the above technique, the first order ratecontent for the standard 46 A.I. silica-alumina catalyst is 63.3seconds⁻¹ at 250° C. This value was arbitrarily assigned an index of1,000 so as to serve as a reference value. Thus, the cyclopropane index(C.P.I. Index) for a candidate catalyst component with a first orderrate constant of 3.165 would be determined as follows: ##EQU2##

Thus, the expressions "substantially non-acidic" and a zeolite which is"virtually free of acidic sites" as used throughout the specificationand claims is intended to define a zeolite which has a C.P.I. Index ofno greater than 50, and preferably no greater than 10, as measured bythe aforementioned test.

The following Table 1 lists the values obtained when subjecting variouszeolites to the cyclopropane isomerization test previously set forth.

    ______________________________________                                        Cyclopropane Isomerization (CPI) Index                                        Catalyst Components  k,sec.sup.-1 250° C.                                                                CPI                                         ______________________________________                                        (1) MgPHZSM-5        151          2400                                        (2) 46 A. I. Si/Al, Ref. Std.                                                                      63.3         1000                                        (3) ZrO.sub.2        60.2          950                                        (4) HZSM-5, SiO.sub.2 /Al.sub.2 O.sub.3 = 1670                                                     50.0          790                                        (5) KHZSM-5          3.98          63                                         (6) NaZSM-5, SiO.sub.2 /Al.sub.2 O.sub.3 = 90                                 (Bx NaHCO.sub.3)     1.36          21                                         (7) NaHZSM-5, SiO.sub.2 /Al.sub.2 O.sub.3 = 1670                                                   0.441        7.0                                         (8) NaZSM-5, SiO.sub.2 /Al.sub.2 O.sub.3 = 600                                                     0.125        2.0                                         (9) NaZSM-5, SiO.sub.2 Al.sub.2 O.sub.3 = 1670                                                     0.050        0.8                                         ______________________________________                                    

From the above Table 1, it can be seen that there are ZSM-5 zeoliteswhich have the requisite C.P.I. Index for the novel process of thisinvention, as well as ZSM-5 type materials in which the C.P.I. Index isso high as to preclude their usefullness herein. Thus, for example,Catalyst Component No. 1 is a magnesium phosphorous exchanged ZSM-5 and,as can be seen, its acidity is higher than the 46 A.I. referencestandard. Catalyst Component No. 4 is an acid exchanged ZSM-5 zeolitehaving a silica-to-alumina mole ratio of 1670 and, as can be seen, thismaterial is also inoperable in the novel process of this invention.Catalyst Component No. 5 is a potassiumn exchanged acid ZSM-5, but itsimply has not been exchanged with enough potassium to lower its aciditysince it has a C.P.I. Index of 63. Catalyst Components 6, 7, 8 and 9 allpossess a sufficiently low C.P.I. Index to be potential candidates forthe novel process of this invention, providing of course that theappropriate metal component is intimately combined with a substantiallynon-acidid zeolite according to this invention.

From the foregoing it is evident that in order to attain the requisitestate of non-acidity, more than one of the aforementioned techniques mayhave to be applied. Thus it may not be sufficient that a high silicazeolite, e.g., SiO₂ /Al₂ O₃ =1600, is utilized, such zeolite may stillhave to undergo base exchange or steaming. Alternatively, the extensivebase exchange of a low silica-alumina zeolite, or the use of a ultrahigh-silica zeolite, e.g., SiO₂ /Al₂ O₃ =30,000, may result in amaterial having the requisite C.P.I. value without any furthertreatment.

A major difference between the instant invention and the heretoforepracticed processes for synthesis gas conversion utilizing zeolitesresides in the fact that the specific products obtainable from thepresent invention will not be generated by a mere physical mixture of amember of the novel class of zeolites and the useful metal. The metalmust be intimately combined with the zeolite. In this connection,methods for including such metals within the pores of zeolites to arriveat an intimate combination are known in the art. The preferred techniquefor achieving such intimate combination is impregnation of the zeolitewith an aqueous solution of a salt of the desired metal. The nature ofthe salt is not critical and any water-soluble salt such as chloride,sulfate and nitrate can be utilized. The zeolite may be soaked or dippedin such a salt solution, or alternatively, the solution can be vacuumsprayed onto the zeolite. The amount of metal in said zeolite can rangefrom between about 0.1 and about 10 wt. percent, preferably from betweenabout 0.2 and about 5 wt. percent.

The useful metal component of the catalyst of this invention is selectedfrom the group consisting of rhodium, platinum, palladium and iridium,the preferred metal component is rhodium.

The catalyst of this invention may be prepared in various ways. Thecatalyst may be prepared in the form of catalyst particles such aspellets or extrudates. The particle size of the individual componentparticles may be quite small, for example from about 20 to about 150microns, when intended for use in fluid bed operation; or they may be aslarge as up to about 1/2 inch for fixed bed operation. Binders such asclays may be added. The component that has catalytic activity for thereduction of carbon monoxide is formed on the zeolite component byconventional means such as impregnation of that solid with saltsolutions of the desired metals, followed by spray drying andcalcination.

In the process of this invention, synthesis gas is contacted with thecatalyst of this invention at a temperature of between about 500° F. andabout 1000° F., preferably from between about 700° F. to 900° F.; at apressure of from between about 10 and about 200 atmospheres, preferablyfrom between about 60 and about 100 atmospheres; and at a gas hourlyspace velocity (GHSV) from between about 100 and about 10,000 volumes ofgas, at standard temperature and pressure per volume of catalyst,preferably from between about 200 and about 2,000 GHSV. The catalyst maybe contained in a fixed bed, or a fluidized bed may be used. The productstream containing hydrocarbons, oxygenates, unreacted gases and steammay be cooled and the hydrocarbons and oxygenates recovered by any ofthe techniques known in the art, which techniques do not constitute partof this invention. The recovered hydrocarbons and oxygenates may befurther separated by distillation or other means to recover one or moreproducts such as high octane gasoline or chemical intermediates.

The concepts and objectives of the present invention are furthersupported by the following examples.

EXAMPLE 1

This example illustrates the preparation of highly siliceous ZSM-5. Thesynthesis of this zeolite involved the combining of four majorcomponents-silicate solution, acid solution, additional solids andadditional liquid.

The silicate solution was comprised of 1 part Q-brand sodium silicate(PQ Company, Philadelphia, Pa.), 0.58 parts water and 0.0029 parts Daxad27 (W. R. Grace Company). The acid solution was composed of 0.10 partssulfuric acid, 0.045 parts sodium chloride, 0.16 parts water and 0.56parts of prereacted organics.

The prereacted organics were prepared by charging the followingmaterials to an autoclave: 0.30 parts methylethyl ketone, 0.18 partstri-n-propylamine and 0.15 parts n-propyl bromide. These materials forthe preparation of the prereacted organics were mixed with gentleagitation for 15 minutes. The agitation was stopped and 1 part water wascharged to the autoclave. The autoclave was sealed and heated to 220° F.and held at 220° F. for 15 hours. After this reaction period thetemperature was raised to 320° F. and the unreacted organics wereflashed off. The aqueous phase was removed containing the prereactedorganics and contained 1.44% wt nitrogen.

The additional solids for this preparation was 0.14 parts sodiumchloride and the additional liquid was 0.029 parts water.

The silicate solution and acid solution were mixed in a mixing nozzle toform a gel which was discharged into an autoclave to which 0.029 partswater had been previously added. The gel was whipped by agitation and0.14 parts NaCl were added and thoroughly blended. The autoclave wassealed and heated to about 220° F. with agitation at 90 rpm and held for54.3 hours until crystallization was complete. The contents of theautoclave were cooled and discharged. The crystallized product wasanalyzed by x-ray diffraction and was found to be 100% wt ZSM-5. Thechemical analysis of the thoroughly washed crystalline product is

    ______________________________________                                                        % Wt  Mole Ratio                                              ______________________________________                                        Al.sub.2 O.sub.3  0.10    1.0                                                 SiO.sub.2         98.3    1670                                                Na                1.6     --                                                  Na.sub.2 O        --      35.5                                                N (as received basis)                                                                           0.75    63.9                                                C (as received basis)                                                                           8.98    892                                                 ______________________________________                                    

EXAMPLE 2

Highly siliceous Na ZSM-5 with a silica to alumina mole ratio of about1600 and impregnated with 0.5 wt. percent rhodium (as nitrate) isrepresentative of a catalyst useful in the instant invention. Thiscatalyst was prepared by dissolving 0.14 grams of rhodium nitrate saltin 15 ml of water and contacting the resultant solution with 10 grams ofhighly siliceous Na ZSM-5 prepared according to Example 1 under vacuumconditions. The sample was then vacuum-dried in a rotary evaporator at atemperature of about 90° C. and further subjected to calcination at 538°C. for 10 hours in an oven. The impregnated Na ZSM-5 was then reduced at195° C. at 1 atmosphere pressure and for 41/2 hours with 30 cc/minute offlowing hydrogen.

EXAMPLE 3

The catalyst prepared according to Example 2 was tested for synthesisgas conversion conducted at 800° F., 1400 psig and 600 GHSV in a fixedbed reactor with 2.93 grams of catalyst. The synthesis gas compositionwas 50 vol.% CO, and 50 vol.% H₂. Gas and liquid products were separatedand analyzed chromatographically. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        *Conversion to Products:                                                                        56%                                                         Product Breakdown:                                                                              74% Hydrocarbons                                                              26% Oxygenates                                              Product was shape-selective, i.e., virtually free                             of C.sub.11.spsb.+  compounds.                                                 Composition of Oxygenates;                                                                        wt. %                                                    ______________________________________                                        Methanol             12                                                       Ethanol              25                                                       C.sub.3.spsb.+  Alcohols                                                                           12                                                       Aldehydes            28                                                       Ketones              2                                                        Esters               6                                                        Acetic Acid          5                                                        Other                10                                                                            100                                                      ______________________________________                                        Composition of Hydrocarbons:                                                                       wt. %                                                    ______________________________________                                        C.sub.1              45.3                                                     C.sub.2              24.4                                                     C.sub.3              18.2                                                     C.sub.4              7.4                                                      C.sub.5              1.6                                                      C.sub.6 to C.sub.10  2.9                                                      C.sub.11.spsb.+      0.2                                                      ______________________________________                                         ##STR1##                                                                 

Having thus generally described the method, catalysts and concepts ofthe present invention and presented examples in support thereof, it isto be understood that no undue restrictions are to be imposed by reasonthereof except as defined by the claims.

What is claimed is:
 1. A catalyst composition for use in convertingsynthesis gas into oxygenate-containing mixtures, which comprises azeolite which is virtually free of acid sites and which has an acidactivity, as measured by the C.P.I. Index, of no greater than 50, andcharacterized by a silica to alumina mole ratio of at least about 12, aconstraint index within the range of 1 to 12, having intimately combinedtherewith a metal selected from the group consisting of rhodium,platinum, palladium and iridium.
 2. A catalyst composition according toclaim 1 wherein said acid activity, as measured by the C.P.I. Index, isno greater than
 10. 3. A catalyst composition according to claim 1wherein said zeolite is selected from the group consisting of ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38.
 4. A catalyst compositionaccording to claim 3 wherein said zeolite is ZSM-5.
 5. A catalystcomposition according to claim 1 wherein said metal is rhodium.
 6. Acatalyst composition according to claim 1 wherein said metal isimpregnated in said zeolite.
 7. A catalyst composition according toclaim 1 wherein said zeolite is rendered virtually free of acid sites bybase exchange of an acidic zeolites.
 8. A catalyst composition accordingto claim 7 wherein said base exchange is carried out with cationsselected from the group consisting of metals from Group IA of thePeriodic Chart, Group IIA of the Periodic Chart and ammonium cations. 9.A catalyst composition according to claim 8 wherein said Group IA cationis a sodium cation.
 10. A catalyst composition according to claim 1wherein said zeolite is highly siliceous and sodium exchanged.
 11. Acatalyst composition according to claim 1 wherein said metal intimatelycombined with said zeolite is in the range of from about 0.1 to about 10weight percent of the total composition.
 12. A catalyst compositionaccording to claim 11 wherein said metal is in the range of from about0.2 to about 5 weight percent of the total composition.